I think the grey of the side stones do pull out the grey from the center stone, but if you’re okay with that /regardless of that, it does look cool!
If I could stretch to the diamonds I’d go the diamond route. If I specifically wanted to set the grey spinal as side stones, I’d probably do this (or maybe set it with a center stone I didn’t mind pulling grey from).
i think the grey really compliments the blue in a different way than diamond side stones would
and its a bonus you already have them on hand